Techniques for determination of rat thymocyte sodium content and 22-Na efflux were validated in this laboratory and used to measure the impact of dietary salt excess on cell sodium homeostasis. Male Sprague Dawley rats were fed either a normal diet (.35% NaCl controls) or high-salt diet (7.5% NaCl experimental) for one week. Control thymocytes were incubated in sera from either control or experimental rats and intracellular sodium content and 22-Na efflux were measured. Both intracellular sodium content and 22-Na efflux were measured. Both sera inhibited ouabain sensitive 22-Na-efflux and stimulated ouabain insensitive 22-Na efflux.